I've lived in the Boston area my entire life, and at the age of 42, I finally went to Kelly's (Natick) last Friday.
Maybe I was really hungry, but I thought it was great. I had a small roast beef sandwich, which was HUGE. The meat was extremely lean. I also had onion rings, which were very greasy, but delicious.
It's really one of the best sandwiches I've had in a long time. Get it with horseradish if you can take it!
Can't wait to go back!